Trigger Port Forwarding Example; Two Points To Remember About Trigger Ports - ZyXEL Communications NBG-417N - V1.0 Manual

Chapter 11 Network Address Translation (NAT)

11.9.1 Trigger Port Forwarding Example

The following is an example of trigger port forwarding.
Figure 71 Trigger Port Forwarding Process: Example
Jane requests a file from the Real Audio server (port 7070).
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Port 7070 is a "trigger" port and causes the NBG-417N to record Jane's computer
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IP address. The NBG-417N associates Jane's computer IP address with the
"incoming" port range of 6970-7170.
The Real Audio server responds using a port number ranging between 6970-7170.
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The NBG-417N forwards the traffic to Jane's computer IP address.
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Only Jane can connect to the Real Audio server until the connection is closed or
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times out. The NBG-417N times out in three minutes with UDP (User Datagram
Protocol), or two hours with TCP/IP (Transfer Control Protocol/Internet Protocol).

11.9.2 Two Points To Remember About Trigger Ports

Trigger events only happen on data that is going coming from inside the NBG-
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417N and going to the outside.
If an application needs a continuous data stream, that port (range) will be tied up
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so that another computer on the LAN can't trigger it.
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NBG-417N
NBG-417N User's Guide